1. Technical Field
The present disclosure relates to an organic electroluminescent device.
2. Description of Related Art
Many are gradually coming to believe that organic electroluminescent devices have the potential to become a leading technology in the area of flat panel displays and in the lighting industry due to their thin profile, light weight, self-emissive property, ability to eliminate the need for a back light source, unlimited viewing angle, and high response speed.
The luminous efficiency of an organic electroluminescent device may be expressed as follows:
      η          Power      ⁢                          ⁢      efficiency        ∝            γ      ×              η        exciton            ×              η        material            ×              η        outcoupling              V  
where ηPower efficiency is the luminous efficiency of the organic electroluminescent device, γ is a recombination ratio of hole and electron carriers, ηexciton is a generation ratio of an exciton, ηmaterial is a quantum efficiency of material, ηoutcoupling is an extraction efficiency, and V is an operating voltage of the organic electroluminescent device.
From the above formula, it is evident that the extraction efficiency is a key factor in the luminous efficiency of an organic electroluminescent device. However, in an organic electroluminescent device, due to the difference in refraction index between adjacent layers, most of the light (approximately 80%) illuminated from the organic electroluminescent device is lost because of total reflectance. Only some of the light (approximately 20%) can be extracted for illumination purposes.
Therefore, there is a need to enhance the light extraction efficiency of an organic electroluminescent device and thereby raise the luminous efficiency thereof.